En el documento de Hansen tampoco entiendo el ajuste por horario (sección 4.1.1) ni el ajuste por categoría en la sección 5.3. Ambas son las que dan un incremento de temperaturas en el periodo 1960-2000 de forma progresiva de +0.3ºC.
Me refería a que la cosa quedaría así después de los ajustes. Si no se hicieran ajustes, tendríamos un calentamiento 0.3ºC inferior y tal vez sin tendencia clara:
http://pubs.giss.nasa.gov/docs/2001/2001_Hansen_etal.pdf
Saludos.
Insisto.
4.1.1. Time of observation bias. The standard way of calculating the monthly mean temperature in the United
States is to define the daily mean as the average of the daily maximum and minimum temperatures and then average the daily means over the month. The preferred 24-hour period would be the calendar day, i.e., from midnight to
midnight. However, most observers recording results from maximum-minimum thermometers prefer observing
times other than midnight. The time of observation has a systematic effect on the monthly mean temperature
[Mitchell, 1958], for example, an afternoon 24-hour reading samples the diurnal cycle near its maximum on 2 days.
This would not matter much if the time of observation at a given station did not change during the station’s history.
However, there have been changes of the time of observation by many of the cooperative weather observers in the
United States [Karl et al., 1986]. Furthermore, the change has been systematic with more and more of the
measurements by United States cooperative observers being in the morning, rather then the afternoon. This
introduces a systematic error in the monthly mean temperature change.
Karl et al. [1986] derived a correction for the time-of-observation bias and verified its validity from hourly
data available for many U.S. stations. Of course, to apply this correction, it is necessary to have reliable metadata
defining all changes of time of observation in the station record. These data generally exist for the USHCN stations
and are believed to be reliable [Karl et al., 1990]. The time of observation correction is one of the two substantial
adjustments included in the adjusted USHCN data [Karl et al., 1990; Easterling et al., 1996a], as illustrated in
section 5 below. This time of observation correction, which is the first in the sequence of adjustments carried out by
Karl et al. [1990], is included in the current GISS analyses for USHCN stations. Such a correction is not generally
required in the rest of the world, because the systematic shift from once a day evening to once a day morning
observations which occurs at U.S. cooperative observer stations is not characteristic of most global observations
[Easterling et al., 1996b]
Quería que me comentaran la corrección que emplea hansen en el apartado "Time of observation bias" tiene lógica. Yo no la encuentro por ningún sitio. Sólo eso hace que la tendencia del calentamiento global suba 0.15ºC. Es extraño que según se van teniendo cada vez más estaciones que indican la media (y no sólo la máxima y mínima), cada vez la corrección sea mayor, hasta llegar al año 2000, donde la corrección es máxima.
¿Actualmente sigue Hansen aplicando esto? o ¿nos fiamos de la temperatura media que marcan las estaciones?.
Saludos.
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